The present invention relates to air pumps and, more particularly, to small, hand-operated air pumps used for inflating game balls, game ball cannisters, and air-filled shock absorbers for motor cycles and the like.
The present invention is primarily directed towards apparatus for enclosing, sealing and pressurizing small containers such as tennis ball cans. Such devices are known in the art such as that exemplified in the patent to Helms (U.S. Pat. No. 3,853,222), FIG. 1 of which is reproduced in part as FIG. 1 of this application. In such a device, the cap, generally indicated as 10, is held in place on the top of a tennis ball can 12 by a collar 14 bearing against the rim 16 of the can 12. A flat gasket 18 which is disposed about the periphery of a sealing plate 20 bears against the rim 16 to seal the can 12. The sealing plate 20 has a hole 22 disposed therein over which is placed a rubber flapper valve 24. The upper portion of the cap 10 comprises a cylinder 26 in which is disposed a piston 28. The outer end of the piston 28 is formed as a gripping handle 30. The inner end of the piston 28 is fitted with a cup gasket 32 which allows air to flow past it on the upstroke of the piston 28 and seals against the side walls of the cylinder 26 on the downward or compression stroke.
Further modifications known in the art are shown in FIG. 2. For example, a release valve 34 is sometimes provided because the gasket 18 as thus configured tends to be so firmly wedged against the rim 16 initially in order to prevent leakage thereof that, once pressurized, it is virtually impossible to remove the cap from the can 12 without first releasing the pressure from within the can. Additionally, an integral gauge, such as that generally indicated as 36, is provided. Gauge 36 comprises a small piston 38 within a closed cylinder 40 which communicates with the inside of the can 12 through the hole 42. An air bubble 44 is trapped within the cylinder 40 above the piston 38 and sealed against leakage by a sealing material 46 such as heavy oil. The air bubble 44 acts as a bias against the piston 38 so that the piston 38 moves and compresses the bubble 44 as the internal pressure of the can 12 increases. Indicia of the pressure level is disposed along the outer surface 48 of the cylinder 40 so that the internal pressure of the can 12 can be determined, approximately, from the position of the piston 38, by visual inspection.
As a safety measure in such apparatus, a large area 50 is provided below the piston 28 within cylinder 26 at the bottom of its stroke thus limiting the amount of pressure which can actually be developed through pumping action. As a consequence, the volumetric efficiency of the pumps of such prior art caps 10 was very low and in order to achieve an internal pressure within the tennis ball can 12 of, for example, 15 psi, several hundred strokes of the piston 28 could be required.
Wherefore, it is an object of the present invention to provide a pumping mechanism for such uses which has a high volumetric efficiency while being safe against over pressurization.
It is yet another object of the present invention to provide a self-limiting pumping mechanism which will automatically cease pumping at a pre-selected pressure.
It is yet another object of the present invention to provide a sealing and pressurization cap for a tennis ball can which seals thereto without leakage while at the same time being removable without the necessity of a pressure release valve.